1. Technical Field
The present invention relates to methods for controlling the composition of a photovoltaic thin film.
2. Discussion of the Related Art
Existing methods for producing a photovoltaic thin film cell utilize annealing in air or in selenium, tellurium or sulfur containing atmospheres.
FIG. 1 illustrates part of an existing method for producing tellurium, selenium or sulfur containing compound semiconductor thin films such as cadmium telluride (CdTe), cadmium selenide (CdSe), cadmium sulfide (CdS), zinc sulfide (ZnS), tin tetrasulfide (SnS4), copper indium diselenide (CuInSe2), copper indium disulfide (CuInS2), copper gallium diselenide (CuGaSe2), copper gallium disulfide (CuGaS2), copper bismuth sulfide (Cu3BiS3), copper sulfide zinc tin tetrasulfide (Cu2ZnSnS4), copper indium gallium diselenide (CuInGaSe2), or copper indium gallium disulfide (CuInGaS2) photovoltaic thin film cells. As shown in FIG. 1, the method includes an anneal step in a sulfur or selenium atmosphere. A copper indium diselenide (CuInSe2) or copper indium gallium diselenide (CuInGaSe2) photovoltaic thin film may lose a light element such as selenium or sulfur during annealing. Although the lost selenium can be replaced after annealing by performing an additional process step, this increases the time, cost and complexity of forming a photovoltaic thin film cell.